Recent emphasis on security has placed higher demands on development of detection of threats, including liquid explosives. Any means for detection for public use must be non-invasive, rapid, and be able to distinguish potential threats from, e.g., beverages or common personal care products. Nuclear magnetic resonance (NMR) techniques have long been used to investigate properties of materials ranging from chemical samples to the human body, referred to as magnetic resonance imaging, or MRI. NMR instruments typically employ large superconducting magnets that produce high magnetic fields.
Ultra-low field magnetic resonance imaging in combination with SQUID (superconducting quantum interference device) detectors has been shown to be capable of non-invasively identifying certain hazardous materials in luggage and shipping containers (see U.S. patent application Ser. No. 11/804,799, filed May 18, 2007). Some advantages of ULF-MRI systems include the lack of requirement of large, powerful magnets, and the ability to analyze materials enclosed in conductive and lead shells. SQUID detectors, while remarkably sensitive, require cryogenic cooling. This results in added expense and size, which significantly limits practical applicability.
A need exists, therefore, for a system for threat detection and discrimination of liquids, in particular of liquid explosives or components thereof, which is sensitive, rapid, non-invasive, and which is also relatively inexpensive and portable.